The turnout was higher than in previous years. Many Mandaeans have been driven out of Iraq by conflicts since the 2003 U.S. led invasion.
Dressed in white robes, these followers of the ancient Mandaean religion slowly lower themselves into the Tigris River.
They're here to purify their souls, in a baptism ritual they have been practising for centuries.
They also wash their kitchen utensils in the river as they believe it will mean that God will bless their food.
Until 2003, nearly all the world's Mandaeans lived in Iraq, but the cycles of conflict since the US invasion have driven minorities out of the country for security reasons and economic opportunity.
But the turnout this year is higher than in previous years. Hundreds of Mandaeans gather in a park on the Tigris River which is owned by the sect.
Sheikh Jabbar Sattar al-Helo, the spiritual leader of the Mandaeans in Iraq, is attending today's ceremony.
He explains how the ceremony is also about celebrating their "beloved dead".
"During these days the barriers are lifted between the dead and the alive, where we are dressed in the white shrouds and we address it and dedicate it to the dead people who were not able to do such rituals. Because in our belief the Mandaean should practise these rituals before he dies. And those who die in an accident and they have not practised them, we are making for them these clothes and we dedicate it to them."
Around 10,000 Mandaeans are left in Iraq today, which is a fraction of previous figures.
Their numbers are particularly susceptible to the toll of migration because Mandaeism does not accept converts: worshippers must be born into the faith.
Al-Helo adds that: "We are noticing the rise of moderate speech and this is what we are looking for on all levels so we all live in peace."
Mandaeism follows the teachings of John the Baptist, a saint in both the Christian and Islamic traditions, and its rites revolve around water.
Today, the Mandaeans immerse themselves in the running water three times to ease the worries of life and relieve any sin they have committed.
Mandaean women practise the ritual along with the men. They are also dressed in white with their heads covered.
One female pilgrim, Nihad Abdulkareem Mohammad, says: "We are not worshipping the water, but we worship the creator. Water is the secret of life and existence."
Iraq's soaring water pollution has posed a threat to the religious rites of the Mandaean community in recent years.
Baghdad's river today is a stew of industrial chemicals, untreated sewage, and poisonous agricultural runoff, the Save the Tigris civil society campaign said in a 2018 report.
And water levels are falling, owing to the changing climate and damming in Turkey, Syria, and Iran. About 70 percent of Iraq's water flows from upstream countries.
